The invention relates to an electromagnetic transducer for the transmission and reception of ultrasonic waves in the touchless testing of metal workpieces, particularly but not exclusively flat strip or sheet metal or ferritic or austenitic steel comprising at least one transducer element having a plurality of mutually parallel conductor tracks formed on a substantially planar printed circuit board.
A transducer of this kind is described in the paper by H. Licht, TH Aachen, 1973 entitled "A potential method of touchless excitation and reception of Lamb waves in electrically conductive plates by a mode-selective electrodynamic transducer system". In order to be able to apply a data-providing mode-spectroscopy to thin work pieces, this previously known transducer comprises exchangeable circuit boards with relatively different conductor-line arrangements or patterns whereby the respective wavelength is determined. Testing frequency on the other hand is continuously adjustable. Whilst this method eventually provides a positive test result from which information can be obtained it is extremely time-taking. In particular, it does not allow continuous mode-spectroscopic testing of material to be made. Besides, there are other interfering influences. Furthermore, there is a limitation in respect of the test samples in the form of thin plates and correspondingly in respect of waveform in the shape of Lamb waves.